1. Field of the Invention
The present invention relates to novel 1,4-benzothiazine-2-acetic acid derivatives having an excellent aldose reductase inhibitory activity and pharmaceutically suitable salts thereof, and processes for production thereof as well as a composition comprising the same. The compounds of the present invention are useful for the prevention and treatment of diabetic complications such as diabetic cataract, retinopathy, nephropathy, neuropathy, etc.
2. Description of the Prior Art
Heretofore blood sugar level regulators such as insulin and synthetic hypoglycemic agents have been widely used as drugs for the treatment of diabetes mellitus. However, diabetes mellitus is a disease which accompanies a variety of complications so that it is difficult to prevent development of these complications simply by controlling blood sugar level alone. It has thus been desired to develop a novel drug for the treatment of diabetic complications. In recent years, attention has been brought to accumulation and increase of sorbitol and galactitol in tissue, which is caused by chronic hyperglycemia, as a mechanism of causing diabetic complications.
It is suggested in publications that compounds which inhibit the activity of aldose reductase as an enzyme of reducing an aldose such as glucose and galactose to convert into sorbitol and galactitol. [cf., J. H. Kinoshita et al., Biohim.] Bophys. Acta, 158, 472 (1968), Richard Poulson et al., Biochem. Pharmacol., 32, 1495 (1983), D. Dvornik et al., Science, 182, 1145 (1973)].
Such aldose reductase inhibitors function by inhibiting the activity of enzyme aldose reductase, which is primarily responsible to regulating the reduction of aldoses, such as glucose and galactose, to the corresponding polyols, such as sorbitol and galactitol, in humans and other animals. In this way unwanted accumulation of galactitol in the lens of galactosemic subjects and of sorbitol in the lens, peripheral nervous cord and kidneys of various diabetic subjects are prevented or reduced.
Accordingly, such compounds are of therapeutic value as aldose reductase inhibitors for controlling certain chronic diabetic complications, including those of an ocular nature, since it is known in the art that the presence of polyols in the lens of the eye leads to cataract formation, with a concomitant loss of lens clarity.
Among the compounds synthesized along with such an example, Japanese Patent Application Laid-Open Nos. 61-40264 and 63-107970 disclose that a variety of 1,4-benzothiazine- 4-acetic acid derivatives possess an aldose reductase inhibitory activity. However, it has been desired to develop a drug for the treatment of diabetic complications having a more excellent aldose reductase inhibitory activity.
In a view of such actual situation, the present inventors have made extensive investigations to develop drugs for the treatment of diabetic complications having an aldose reductase inhibitory activity. As a result, it has been found that the object can be achieved by certain benzothiazine derivatives and the present invention has been accomplished.